Polio has been spreading widely for a year, and was present in New York’s wastewater as early as April, according to a new report from the Centers for Disease Control and Prevention.
A wastewater sample collected in April in Orange County, NY, tested positive for the virus, pushing back the earliest known detection in the area. Officials previously announced that the virus had been detected in samples of wastewater in neighboring Rockland County in May.
Changes in the virus’s genome suggest that this variant has been circulating somewhere in the world for a year. Genetically identical versions of the virus were detected in Israel in March and the UK in June.
The new study provides more details from an ongoing investigation into a case of polio detected in New York last month after officials announced that a young adult in Rockland County had been paralyzed by polio. This was the first report of polio in the United States since 2013.
The findings are not entirely surprising, especially considering that polio, which is highly contagious, often spreads without causing serious symptoms, said Joseph Eisenberg, an infectious disease epidemiologist at the University of Michigan. “It may have been very widely circulated, being under the radar, before we really started seeing cases of paralysis,” he said.
Officials previously warned that the Rockland County patient was “the tip of the iceberg.”
The new study showed that the polio vaccination rate in some of the county’s zip codes is just 37 percent.
According to the study, a patient who was not vaccinated against polio was hospitalized in June after developing symptoms including fever, stiff neck and weakness in the lower limbs. The poliovirus, which is mainly transmitted through faeces, was later detected in the patient’s stool.
Genomic sequencing revealed that the patient was infected with a variant of the virus derived from the oral polio vaccine, which contains a weakened version of the virus. The oral vaccine has not been used in the United States since 2000. (American children are routinely immunized with the injected vaccine.)
The oral vaccine is safe and effective, but people who get it can shed the weakened virus in their stool for weeks, potentially infecting others. In communities with many unrelated people, the virus can spread and eventually acquire enough mutations to be dangerous again.
The discovery of the Rockland case prompted health experts to begin testing samples of wastewater collected in the region, including those previously collected for coronavirus surveillance.
Officials previously announced that they had found the virus in 20 wastewater samples collected in Rockland and Orange counties and all had been genetically linked to the patient’s sample.
The new study showed that the 21st sample collected in Orange County in April also tested positive for the virus. However, not enough genomic information was available to conclusively link it to other samples.
According to the new study, two hundred and sixty-two wastewater samples from Rockland and Orange counties were tested as of August 10, and polio was detected in 8 percent of them.
“This shows that there are a lot of community spread under the radar,” John Dennehy, a virologist at Queens College and a wastewater monitoring expert, said in an email.
The virus has also been found in six wastewater samples from New York City.
The Rockland County patient was most likely exposed to polio one to three weeks before developing symptoms, the report said. According to the study, the patient did not travel abroad during this time, but attended “a large gathering”.
Polio was detected in wastewater in Rockland County 25 days before the patient developed symptoms, suggesting that others were already infected.
“The fact that we see it in sewage 25 days ago means it probably isn’t even a second case,” Dr. Eisenberg said.
People who have received three doses of inactivated polio vaccine are well protected against the virus, but the virus poses a potential risk to people who are too young to be vaccinated, including children.
Nationally, the polio vaccination rate is relatively high. But there are parts of the country, including New York, where vaccination rates are very low, and the pandemic has pushed back childhood vaccination campaigns.
According to the study, as of July 2020, 67 percent of children over the age of 24 months in Rockland County had received three doses of the polio vaccine, which fell to 60 percent by this month.
After the Rockland County case was discovered, the local health department launched a vaccination campaign, but the number of shots given was “not enough to meaningfully increase” vaccination rates, the researchers reported.
(This story has not been edited by seemayo staff and is published from a rss feed)